1. Field of the Invention
The present invention relates to a laser control apparatus, an image forming apparatus for forming an image with light emitted from a laser, and a copier incorporating the image forming apparatus.
2. Related Background Art
The applicant of the basic application filed in Japan filed Japanese Patent Application Laid-Open No. 7-199096 to disclose the invention of the image forming apparatus for forming an image with laser light emitted from a plurality of laser sources, which is provided with a means for controlling laser beams emitted in time division from the laser sources, at a constant light amount by use of light amount detectors numbering less than the number of laser sources.
In this invention, electric current supplied to the laser sources is controlled in order to control the laser beams emitted from the laser sources at the constant light amount, and in this control, where a value of the electric current to be supplied reaches a region where the laser sources can be destroyed, there is no way of limiting it. Potential causes of the increase in the electric current to be supplied include a malfunction, a breakdown, etc. of circuitry in a control system. In such events, the control system sets high electric current to be supplied to the laser source, so that the laser source may be damaged.
An object of the present invention is, therefore, to protect the laser sources from the breakdown, by regulating the electric current flowing in the laser source whenever the means for adjusting the amount of light from the laser source is about to supply the electric current high enough to destroy the laser source, to the laser source.
A laser control apparatus according to the present invention comprises a light source, light amount detecting means for detecting an amount of light emitted from the light source and outputting a light amount detection value, sample and hold means for sampling and holding the light amount detection value, light amount control means for carrying out a negative feedback control of the light amount in accordance with a difference between the light amount detection value and a reference value during a control period in which the light source emits the light and in which the light does not effect writing of a photosensitive member, first comparing means for comparing the light amount detection value with a predetermined value and outputting a first effective comparison output only when the sample and hold means is in a sample state, electric current detecting means for detecting an electric current flowing to the light source and outputting an electric current detection value, electric current detection value holding means for holding an increased value of said current detection value in the control period of the light amount control means, second comparing means for comparing the increased value held by the detection value holding means with a present value of said current detection value and outputting a second effective comparison output only when the sample and hold means is in a hold state, and current interrupting means for interrupting the electric current flowing to the light source in accordance with the first or second effective comparison output.
The laser control apparatus according to the present invention comprises plural sets of the light source, the sample and hold means, the light amount control means, the first comparing means, the current detecting means, the current detection value holding means, the second comparing means, and the current interrupting means, the number of the light amount detecting means is smaller than the number of light sources, and the light amount detecting means is utilized in time division.
An image forming apparatus according to the present invention is an image forming apparatus for writing image data on a photosensitive member with the light emitted from the light source, converting the image data into a visible image, and transferring the visible image onto a transfer sheet to form an image thereon, using the above laser control apparatus.
A copier according to the present invention is one comprising the above image forming apparatus.